Voluminous continental growth of the Altaids and its control on metallogeny

ABSTRACT The Altaids is generally considered to be the largest Phanerozoic accretionary orogen on Earth, but it is unclear whether it was associated with extensive continental crustal growth and whether there is a link between the crustal growth and ore mineralization. This paper reviews whole-rock Nd and zircon Hf isotope data for felsic–intermediate–mafic igneous rocks in the Altaids and presents Nd + Hf isotopic contour maps for this region. The maps highlight the 3D lithospheric compositional architecture of the Altaids and make it possible to quantitatively evaluate the crustal growth and its relationship with ore deposits. The Altaids hosts ∼4 107 350 km2 and ∼184 830 750 km3 (assuming a crustal thickness of 40–50 km) juvenile crust (ϵNd(t) > 0), accounting for 58% by isotope-mapped area (∼7 010 375 km2) of almost all outcrops of the Altaids (∼8 745 000 km2) and formed during 1000–150 Ma (mainly 600–150 Ma). The juvenile crustal, slightly juvenile-reworked crustal and slightly reworked crustal provinces controlled the Cu–Au, the Pb–Zn–Ag and the Li–Be, Nb–Ta and W–Sn ore deposits. According to the crustal architecture and background of deep compositions, we propose that the ore deposits can be grouped into three types: juvenile crust-related, mixed-source (or slightly juvenile crust)-related and reworked crust-related. This highlights the close relationship between accretion, continental growth and mineralization, and will facilitate exploration for specific ore-deposit types in the Altaids.


INTRODUCTION
Earth is the only planet in the Solar System known to have a granitic (felsic) continental crust [1]. The continental crust records Earth's history and hosts mineral resources [2][3][4]. The growth and reworking of the continental crust, and its link to ore resources are some of the most contentious areas of Earth Sciences and essential to understanding the origins of the metallic resources [5][6][7][8][9][10][11][12][13]. Continental crustal growth refers to the addition of mantle-derived materials (e.g. magmas) and their differentiation products to the continental crust via a range of geological processes, which increase the crustal area and volume [14,15]. It is generally considered that converging plate margins where ocean crust is subducted beneath continents are the most important sites for crustal growth, such as island arc accretion belts in the West Pacific (e.g. the Japan arc), the Cordilleras in North America and multiple oceanic subduction systems in Indonesia [13,16,17]. However, the onset time of plate tectonics is controversial, ranging from Hadean to Phanerozoic (e.g. [18]). Some models suggested that there may have been huge crustal growth early on [13,19,20].
In addition, numerous studies have argued that subduction can also cause crustal consumption [4,21,22]. At denudation-or advancing-type subduction zones, crustal materials can be transported into the mantle. Therefore, it is generally thought that continental growth has been <10% of the entire continental crust or almost zero since the Phanerozoic during which modern plate tectonics C The Author(s) 2022. Published by Oxford University Press on behalf of China Science Publishing & Media Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. was dominated and ∼80%-90% of the continental crust had formed by the early Precambrian prior to 1.8 Ga [2,4,23,24].
The identification of significant crustal growth in the Phanerozoic Altaids [25][26][27], or the Central Asian Orogenic Belt (CAOB, [28][29][30]), challenges this concept [28,[31][32][33]. Şengör et al. [25] speculated that nearly 50% of the Altaids may be juvenile. This was evidenced by the study of voluminous granites and their primitive isotopes [28,31,[34][35][36][37][38][39][40][41]. Thus, the Altaids is considered to be Earth's largest Phanerozoic accretionary orogen and also the most important site of Phanerozoic crustal growth [25][26][27][28][29]31,42,43]. More recently, Kusky and Şengör [44] took the Altaids as the largest preserved Phanerozoic juvenile crustal region to compare it with the Archean Superior Province of the North American Craton to test for similarities or differences in the formation of continents through time and to confirm the onset time of accretionary orogenic systems and plate tectonics in the Archean Eon. On the other hand, the Altaids also comprises numerous ancient crustal blocks and microcontinents [45][46][47][48][49]. Even in the juvenile crustal regions, an increasing number of ancient materials have been identified. Therefore, some previous studies proposed that the volume of the crustal growth in the Altaids may have been overestimated and the Altaids is not different from other orogens [46,47]. Consequently, whether or not voluminous crustal growth occurred in the Altaids remains controversial. In addition, the Altaids contains numerous giant ore deposits [9,32,[49][50][51][52], which are unlike those in Cenozoic subduction zones (the North American Cordillera and the Andes) and collisional settings (the Tethyan Himalaya). Many studies have been carried out on the ore deposits in the Altaids, but most have focused on porphyry (Cu) deposits [36,[50][51][52][53][54]. The complex accretionary architecture of the Altaids, particularly the variable types of crust and their link to the ore deposits, remains unclear.
In this paper, we review 5507 whole-rock Sm-Nd and 39 514 (2443 samples) zircon Lu-Hf isotope analyses of igneous rocks as well as 1830 magma-related metallogenic data from the Altaids. We generate isotopic maps for felsic-intermediatemafic igneous rocks in different periods. We use the maps to define the spatio-temporal distribution and relative proportions of juvenile and ancient crust provinces, and to delineate the 3D lithospheric architecture of the Altaids and how it has evolved through time. Our results indicate that extensive Neoprotozoic-Phanerozoic crustal growth occurred in the Altaids. Based on this, the relationship between the (juvenile and reworked ancient) crust and ore-deposit formation is discussed.
The long-lived accretionary and postaccretionary orogeny produced voluminous igneous rocks (mostly granitoids), which account for ∼50%-70% of the present outcrop of the Altaids [28,31,62] (Fig. 1). All these igneous rocks in the western and southern Altaids were mostly generated during the syn-orogenic period (600-250 Ma) and a few during post-orogenic (240-200 Ma) [62,63] in the Paleo-Asian Ocean regime. Many late Paleozoic-Mesozoic igneous rocks in the eastern Altaids were formed by the subduction/accretion (350-150 Ma) of the Mongol-Okhotsk Ocean. A few of the rocks (150-120 Ma) were produced in a post-collisional setting.

Nd + Hf isotopic mapping
A database of whole-rock Sm-Nd (n = 5507 with ages) and zircon Lu-Hf (n = 2443 samples and 39 514 individual data) isotope data for  Tables S1 and S2). These data are available and were used to conduct a series of isotopic maps. The isotopic mapping covers ∼7 010 375 km 2 , including almost all the outcrops of the Altaids, except the largest Cenozoic basin of the northwestern Altaids.
The major orogeny, particularly major magmatism, in the Altaids occurred from ∼600 to 150 Ma (see above). Therefore, Nd and Hf isotopic data of this period were selected and compiled to construct isotopic maps. To obtain more isotope data for mapping, isotope data for igneous rocks older than 600 Ma and younger than 150 Ma were also used, but the isotopic parameters (e.g. ε Nd (t) and model ages (T DM )) were recalculated to ages of 600 and 150 Ma, respectively (Supplementary Tables S1 and S2).
Neodymium isotope contour maps of ε Nd (t) (Fig. 2a) and two-stage Nd depleted mantle model ages (T DM2 ; Fig. 2b) were conducted for the Altaids. The ε Nd (t) and T DM2 values exhibit large variations (Supplementary Table S1) but a good linear correlation ( Supplementary Fig. S1). So both maps have a similar pattern.
We also produced zircon Hf isotope (ε Hf (t)) and Hf depleted mantle model age (T DM2 ; Ga) maps (Supplementary Table S2 and Supplementary  Fig. S2). As the ε Hf (t) and Hf T DM2 values have a good linear correlation: y = -60.702x + 1228.4, R 2 = 0.988 ( Supplementary Fig. S3), the maps of the ε Hf (t) and Hf T DM2 values are almost the same in an isotopic province pattern (Supplementary Fig. S2a and b).
From a statistical analysis of 220 samples, we obtained good linear correlations between ε Hf (t) and ε Nd (t) values, with ε Hf (t) = 1.0652 × ε Nd (t) + 5.9766 for the intermediate-felsic igneous rocks ( Supplementary Fig. S4) and ε Hf (t) = 1.0132 × ε Nd (t) + 7.1354 mafic rocks ( Supplementary  Fig. S5), which are consistent with those of Huang et al. [64]. These correlations have a similar slope to that of the proposed terrestrial array (y = 1.36x + 2.95; Vervoort et al. [65]) despite the small difference in the intercept. Based on these equations, the ε Hf (t) values can be converted into ε Nd (t) and viewed as equivalent to corresponding ε Nd (t) values for isotopic mapping.
In general, an ε Nd (t) value of 0 separates juvenile and evolved crust [14,66]. Based on the equations, an ε Hf (t) value of +6 is equivalent to an ε Nd (t) value of 0 and distinguishes juvenile and evolved crust. As a result, the whole-rock Nd and zircon Hf isotopic maps show the same or similar isotopic province patterns ( Fig. 2 and Supplementary Fig. S2). Both the Nd and Hf isotopic maps are similar to our maps for xenocrysts and inherited zircons in igneous rocks, revealing the same patterns of juvenile ancient crustal distribution in depth [67]. In this way, we combined Nd and Hf data to produce Nd + Hf isotopic mapping to ensure enough sample data for the isotopic mapping (Fig. 3), particularly for the 3D and 4D mapping (Fig. 4).

Crustal architecture and its evolution
The primitive and evolved isotopic provinces reflect the distribution of juvenile and reworked ancient crust. Province I is characterized by juvenile accretionary complex (i.e. mélange), including intra-oceanic arcs (most contain boninites), accreted oceanic islands and oceanic basalts. This highly juvenile crust has been recognized in many areas (e.g. Western and Eastern Junggar, Inner Natl Sci Rev, 2023, Vol. 10, nwac283 Mongolia in China, southern Mongolia, the Lake zone of northwestern Mongolia and the southern Great Xing'an Range) [46,47,60,[68][69][70].
Provinces II and III include juvenile and slightly juvenile crustal regions such as north Tianshan and southern Mongolia. Province IV represents intact or reworked microcontinents or old terranes, such as the central Altai. Province V is mainly old microcontinents or blocks, such as the Precambrian Erguna, South Tianshan, Central Mongolian and South Mongolian microcontinents. Province VI corresponds to cratons and microcontinents (e.g. the North China Craton and Tuva microcontinents [48]).
The isotopic mapping of igneous rocks is an approach that allows basement terrane mapping [38,71]. In general, intermediate-felsic igneous rocks are derived from the middle-lower crust and mafic igneous rocks are derived from the mantle. Therefore, isotopic mapping of intermediate-felsic and mafic igneous rocks reflects the composition of the middle-lower crust and mantle, respectively. As such, we examined the crustal compositional architecture and its evolution using these two types of rocks and their different ages (Fig. 4).
The juvenile crustal provinces correspond to depleted mantle regions (Fig. 4). This suggests that the depleted mantle provided the material for crustal growth. The evolution from the syn-accretionary (600-320 Ma) to post-accretionary (320-250 and 250-150 Ma) periods indicates that the juvenile crust formed mainly in the accretionary periods (Fig. 4a). This indicates that horizontal crustal growth during accretion was significant and that it did not result in the destruction of the overall crustal architecture. Figure 4b shows a similar pattern to Fig. 3a because the post-accretionary igneous rocks have similar primitive isotopic signatures as the syn-accretionary igneous rocks. The primitive isotopic signatures of the post-accretionary and/or intraplate igneous rocks were either inherited from the earlier syn-accretionary juvenile crustal sources (i.e. there was no new crustal growth) or derived from new mantle-sourced materials (i.e. there was new vertical crustal growth). The latter possibility has been confirmed by numerous previous studies [34,72]. For example, in the eastern Tianshan, the post-accretionary or intraplate (220-200 Ma) granitoids exhibit more primitive signatures (ε Nd (t) = -3 to +0.8) than the syn-accretionary (450-430 Ma) granitoids (ε Nd (t) = -5.8 to -15.8) in the same region [73]. This indicates that new juvenile crustal material was added to the deep crust (i.e. vertical crustal growth) by underplating of mantle-derived magma in a post-accretionary and intraplate setting [73].

Geophysical evidence
The results of the isotopic mapping are consistent with geophysical data. For example, shear wave (Vs) seismic tomography at the depths of 30-40 km, based on >200 stations, identified a high-velocity body in the western Junggar orogen and low-velocity bodies in the Altai and Tianshan mountains (Fig. 5). These coincide with Provinces I and II in the western Junggar orogen and evolved Provinces V and IV in the Tianshan and Altai mountains (Figs 2-4). Furthermore, magnetotelluric imaging identified deepseated Paleozoic paleo-oceanic crust in the western Junggar orogen [74,75]. These features reveal that juvenile oceanic crust-like (i.e. mafic) materials occur in the western Junggar orogen and reworked crust occurs in the Altai and Tianshan mountains.

Nature of the basement of the Junggar Basin: ancient or juvenile?
The Junggar Basin is the second largest basin of the Altaids. The nature of the basement of the basin is controversial, although the basement of the Western and Eastern Junggar orogens is considered to be juvenile (i.e. not Archean-Proterozoic basement [34,67,76,77]). It is generally thought that the basin has a Precambrian (i.e. Archean-Proterozoic) basement [78]. However, others have suggested that the basement could be young and possibly comprises Paleozoic orogenic systems [77,79]. Resolving this controversy requires an evaluation of the area of juvenile crust and the extent of continental growth in the Altaids.
The isotope mapping and geophysical data demonstrate that the basement of the Junggar Basin is mainly juvenile crust, which is similar to that of the peripheral Paleozoic orogen. First, igneous rocks from numerous drill holes in the basin have primitive isotopic characteristics (ε Nd (t) = +2 to +6; median zircon ε Hf (t) = +4 to +9; Figs 2 and 3), similar to those of igneous rocks around the basin. Second, Vs values in the basin at the depths of 30-40 km have revealed a high-velocity body, which is the same or similar to the Vs values at the same depth in the peripheral (i.e. Junggar) Paleozoic orogens. In addition, Zhu et al. [80] used magnetic data to identify numerous strong positive anomalies that trend NNE-SSW in the northwest, NW-SE in the southwest and NE-SW in the center of the Junggar Basin. They interpreted these to be paleo-suture zones consisting of faults, linear tectonics belts or igneous bodies [80]. These features, together with gravity and crustal-thickness data, strongly suggest that the basement has similar geophysical properties to oceanic and mafic lower  crust. All these geophysical studies are consistent with the presence of subducted oceanic crust in the West Junggar orogen [74,75]. Third, our Nd and Hf isotopic mapping, together with xenocrystal zircon mapping of igneous rocks, in the eastern and western Junggar orogens shows no evidence of pervasive ancient continental crustal basement [67,76]. Based on the above discussion, the basement of the Junggar Basin is likely juvenile accretive complexes (e.g. ophiolite mélanges and oceanic crust), which are dense and highly magnetic, similar to the surrounding orogenic belts and their basement. Even if the basin once had ancient Precambrian basement rocks, this basement has been destroyed and only remains as numerous small fragments.

The growth and preservation of the voluminous continent
Based on our isotopic maps, we obtained the relative areal proportions of primitive and evolved isotopic compositions and used these to determine the juvenile and reworked crustal provinces, respectively. This allowed us to quantitatively estimate the volume and extent of continental growth.
Provinces I-III reflect juvenile crust (ε Nd (t) > 0; T DM2 < 1.0 Ga). Its total area is 4 107 350 km 2 , which accounts for 58% of the surface area of the Altaids (all isotopic provinces; Figs 2 and 3). Assuming that the deep-seated juvenile crust represents the entire crust (i.e. there is little significant over-thrusting) and based on a crustal thickness of 40-50 km in the Altaids [81], we estimated the juvenile crust has a volume of 184 830 750 km 3 . If 1000-150 Ma is assumed as the duration for the formation of the juvenile crust, the crustal growth rate is estimated to be ∼21.74 M km 3 /100 Ma (0.22 km 3 per year); and if 600-150 Ma of the timing of the major orogeny is considered, the rate is estimated to be 41.07 M km 3 /100Ma (0.41 km 3 per year). The rate is higher than those estimated in other regions and orogens such as 0.15 km 3 per year of the central Altaids (Mongolia; [37]), 0.016 km 3 per year of the Chinese Tianshan (northern Xinjiang; [41]) and 0.234 km 3 per year of the part of the North American Cordillera (five of the major terranes plus the Coast Mountains batholith [82]). All these appear to be <1.0 km 3 per year-the rate commonly assumed for the worldwide Mesozoic-Cenozoic arc addition rate [83]. All these parameters reflect overall crustal growth.
Moreover, from Fig. 4a, we obtained 3 156 900 km 2 and 142 060 500 km 3 (with the crustal thickness of 40-50 km) of the juvenile crust formed during 600-320 Ma, which accounts for 45% of the surface area of the Altaids (all isotopic provinces). The crustal growth rate is then esti-mated to be ∼50.74 M km 3 /100 Ma (0.51 km 3 per year). These largely reflect the syn-accretionary (horizontal) crustal growth. Subtracting these from the overall crustal growth, we can get the parameters of the left post-accretionary (320-150 Ma) vertical crustal-growth parameters: 950 450 km 2 and 42 770 250 km 3 (crustal thickness of 40-50 km) of the juvenile, accounting for 14% of the surface area of the Altaids (all isotopic provinces; Fig. 4b), which are the largest estimations of the post-accretionary juvenile crust since accretion probably occurred in some regions (e.g. the southeastern Altaids) during this period. The crustal growth rate is then estimated to be ∼61.10 M km 3 /100 Ma (0.61 km 3 per year). These results demonstrate that the syn-accretionary (horizontal) crustal growth dominated in the overall crustal growth in the Altaids.
Using the same method, we also estimated the overall proportions of juvenile crust in other typical accretionary orogens: the North American Cordillera contains ∼54% juvenile crust; the Newfoundland Appalachians contains ∼40% juvenile crust; the Lachlan fold belt contains ∼31% juvenile crust. Collisional orogens contain much less juvenile crust, such as the Tethyan Tibet (3%), Caledonides Variscides (<2%) and Qinling-Dabie (<2%). Compared with these eight orogens, the Altaids shows the highest percentage (∼58%) and largest volume of juvenile crust. Moreover, the Altaids has the highest percentage of highly juvenile provinces with ε Nd (t) value > +4 that formed during the Phanerozoic time. Therefore, the Altaids is the most important site of Phanerozoic crustal growth and the largest preserved Phanerozoic juvenile crustal region. Kusky and Şengör [44] compared the map patterns, lithological contents, and structural and metamorphic evolution of the Altaids with those of the Archean Superior Province of the North American Craton to test for similarities or differences in the formation of continents through time. In addition, the comparison of crustal patterns and volumes of the two tectonic units is also significant. Isotopic mapping is a powerful tool to accomplish this. We use the areas of the isotopic provinces and domains to make a new crustal-growth curve (Fig. 6) and the curve directly and quantitatively denotes the proportions of juvenile and ancient crust and crustal growth. This method is different from other commonly used methods and crustal-growth curves are constructed from cumulative frequency plots of global isotopic data sets [2,4,23,[83][84][85] or by analysis of igneous rock volumes and isotopic data [41,86].
The crustal curve of the Altaids is distinct from that of other orogens and the global curve, indicating a large volume and rapid crustal growth occurred during the Neoproterozoic-Phanerozoic (1000-100 Ma), particularly from 600 to 150 Ma. The growth rate is higher than any other Phanerozoic orogens (see above). As such, the accretionary orogen of the Altaids resulted in voluminous crustal growth from 1000 to 100 Ma, particularly from 600 to 150 Ma. This is consistent with the fact that slab rollback accretion and/or subduction was dominant in the Paleo-Asian Ocean [25,30,43] and Mongol-Okhotsk Ocean domains (e.g. [61]). This also confirms that slab rollback or subduction retreat and accretion are major mechanisms for continental crustal growth [25,87].
More significantly, the preservation of juvenile crust is direct evidence for the voluminous crustal growth [88][89][90]. Numerous oroclines with different sizes have been identified in the Altaids [25,26,43,91]. These oroclines had a key role in the preservation of the juvenile crust, such as the Mongolian orocline [61]. For example, the oroclines contain many trapped structures that preserve a large proportion of the oceanic crustal systems and other types of juvenile continental crust, such as the Junggar region of NW China [69,77,92] and the Lake zone of Mongolia [70] of the western Altaids.

CONTROLS ON MINERALIZATION
The Altaids hosts many world-class, giant mineralization belts, including a porphyry Cu-(Au)-(Mo) ore system and other polymetallic magmatichydrothermal ore deposits, such as Li-Be, Nb-Ta, W-Sn and Pb-Zn deposits [32,36,49,52,53]. The ore-deposit belts were formed during several periods, including the early (490-440 Ma) and late (330-300 Ma) Paleozoic, and Mesozoic (220-190 and 160-120 Ma), in the syn-accretionary, post-accretionary and intraplate settings related to the Paleo-Asian Ocean and Mongol-Okhotsk Ocean tectonic domains [30,43,52]. As such, the mineralization domains in the Altaids can be divided into two parts influenced by the two dynamics. Their extent and boundaries during different periods have been recognized ( Fig. 1; [61]). In addition, the far-field effects of the Paleo-Pacific (or Izanagi) Plate subduction were also superimposed on the eastern Altaids during the Mesozoic.
Our isotope mapping indicates that most of these ore deposits were controlled by the lithospheric architecture and specific crustal types, regardless of where they occur. Figure 7 quantitatively demonstrates the controls of highly juvenile and slightly juvenile-mixed lithospheric architecture on deposit systems, by showing the density of each type of ore deposit in each isotopic province. Most of the deposits are distributed in primitive-slightly evolved isotopic provinces (Provinces I-IV) and at least three peaks in number are prominent (Fig. 7).

Ore-deposit systems associated with juvenile crustal and depleted mantle
A suite of porphyry-type Cu-(Au)-(Mo) deposits, including world-class deposits such as those at represent T DM2 values corresponding to ε Nd (t) = 0; and the dotted horizontal lines denote the percentages of the crust when ε Nd (t) = 0 (e.g. ∼58% of the juvenile crust had been generated at ∼1000 Ma). (d) Other commonly used crustal growth curves are based on a summary by Hawkesworth et al. [2]. The data are listed in Supplementary Tables S1 and S2. Kounrad, Aktogai, Kal'makyr, Oru lolhai and Chalukou, occur in the southern Altaids ( Fig. 7a  and b; [50][51][52]). Based on their ages, locations and dominant ore minerals, these deposits can be further grouped into the western, central and eastern mineralization belts or provinces: (1) the Kazakhstan Cu-Au-Mo belt in the west; (2) the Mongolia Cu-Au in the central area; and (3) the northeast China Mo-Cu in the east, respectively, displaying more Cu deposits in the west and more Mo deposits in the east [52]. Our isotopic mapping demonstrates that the regions of the western and central belts are dominated by large, highly primitive isotopic provinces (Provinces I and II) and the eastern belt is dominated by primitive isotopic provinces (Provinces II, III and some IV). Most porphyry-type Cu-(Au)-(Mo) deposits occur in the Paleo-Asian Ocean domain, which contains more juvenile crust province (Fig. 3). This deep crustal architecture controls the nature of the three mineralization belts.
Moreover, the porphyry Cu and Au deposits are clustered almost exclusively in the primitive isotopic provinces (Province II; i.e. juvenile terranes or crust; Fig. 7a and b). This suggests that the porphyry Cu-Au deposits were mostly related to the juvenile crust, such as the Early and Late Paleozoic (Late Carboniferous) porphyry Cu-Au-Mo deposits in Balkhash in the western Altaids and the Early Paleozoic Cu mineralization in the Duobaoshan (∼480 Ma) and Bainaimiao (∼440 Ma) in the eastern Altaids [36,[50][51][52][53]. This is particularly the case for the largest porphyry Cu system (i.e. the Oyu Tolgoi Cu deposit in southern Mongolia), which was genetically associated with the ∼375-Ma intra-oceanic arcs within the Paleo-Asian Ocean (PAO; [51,53]). Some porphyry Cu and Au deposits around some regions of the Mongol-Okhotsk suture were generated in a continental arc setting (e.g. the Erguna terrane) and they are located in slightly evolved isotopic provinces (Provinces IV; Fig. 7b).
Whether the ore-forming magmas of (porphyry Cu-) Mo deposits in the Altaids have a genetic link with specific deep crustal component(s) is still unclear. Some researchers proposed that relatively ancient crust sources facilitated the formation of the porphyry Mo ore systems (e.g. [36]); others argued for the importance of magma volume (e.g. [93]). Figure 7 shows that the (porphyry Cu-) Mo deposits show more evolved isotopic provinces (in Province IV) and reworked crust than the porphyry Cu-Au deposits (mainly in Province II; Fig. 7a and b), although the Mo deposits have relatively primitive isotopic signatures compared with the Mo deposits in collisional orogenic belts [10]. This indicates that the (porphyry Cu-) Mo deposits in the Altaids have closer relationships to the more reworked ancient crust.
Our Nd-Hf isotopic mapping in the Qinling orogen, central China, also demonstrated a similar correlation [94]. The northern part of the Qinling orogen has a very old basement that is propitious to the development of large and numerous Mo deposits [94]. So, these relationships between the reworked crust and porphyry Mo deposits are the same or similar to previous reports that porphyry Cu-(Mo) deposits commonly occur in more mature continental arc environments compared with gold-rich porphyry Cu deposits in more primitive intra-oceanic arc settings (e.g. SW Pacific; Central and Northern Chile; [95]).
These observations suggest that the deep lithospheric architecture had a key control on these ore systems, despite the role of other factors (e.g. water content, intra-crustal magmatic differentiation, oxidation state and magmatic flux). These support the conclusion that (porphyry) Cu-Au deposits are closer to magmatic arcs (particularly to intra-oceanic arcs) and (porphyry) Cu-Mo to reworked continental margins. Our observations are consistent with those of previous studies of the Altaids [36,52] and other orogens, such as the central Andes [96] and Tethyan Tibet [97].
Most porphyry Cu and Cu-Au deposits in the Altaids were formed in subduction-related settings and close to the arc systems. Four representative genetic models for porphyry magmas associated with porphyry Cu-Mo-Au mineralization have been used to interpret the origin of these deposits [52], i.e. MASH model, 'slab-melting' model, 'preenriched mafic lower crust and subduction of relict mid-oceanic ridges' model and 'melting of juvenile lower crust' model. All the models mentioned above invoke pre-or syn-mineralization injections of juvenile, water-rich materials to the lower crustal levels and explain the dominant occurrence of porphyry Cu-Mo and Cu-Au deposits in juvenile domains.
In addition, mantle-derived deposits such as ophiolite-related Cr and mafic intrusion-related Ni-Cu sulfide deposits are concentrated in the juvenile crustal region (Provinces I and II; Fig. 7a and b), which is underlain by extremely depleted mantle provinces. The Ni-Cu and Cr deposits in the Altai and Junggar orogens are typical for these deposits.

Ore-deposit systems associated with reworked crust
Many large-scale critical deposits with Li-Be, Nb-Ta and W-Sn deposits also occur in the Altaids. These deposits are mainly localized in evolved isotopic provinces (i.e. revoked crust or terranes; Provinces III, IV and V; ε Nd (t) = -4 to +2, peaks at ε Nd (t) = -1; Fig. 7a and c). For example, a worldclass rare metal mineral (Li-Be, Nb-Ta) province occurs in the Great Altai orogen (Mountains) across China, Mongolia, Russia and the border areas of Kazakhstan. This includes the Keketokay No. 3 pegmatite deposit in Chinese Altai, which is the largest pegmatite rare metal deposit worldwide. All these critical metal deposits in the Great Altai orogen, regarding less in the Paleozoic (400-360 Ma) syn-accretionary, post-accretionary late Paleozoic and the early Mesozoic (252-180 Ma) intraplate settings, are almost distributed in the central Altai tectonic unit, i.e. reworked ancient continental fragments, characterized by relative evolved isotopic province with ε Nd (t) values of -2 to -4 (Figs 7a and c, and 8; Province IV). The major reason is that all these rare earth metal deposits are related to the Stype granites and pegmatites that are mainly derived from sedimentary crustal materials characterized by evolved isotopic signatures. Accordingly, the more evolved ancient crustal region is more beneficial for the generation of these deposits. We predict that the Qinghe-Halong region in the southeastern Altaids could be a highly prospective region for such deposits, based on our xenocrystic zircon mapping that identified abundant ancient crustal materials amongst the basement rocks [67,98]. It should be mentioned that all these rare metal mineral deposits in the Altai show a more juvenile crustal background than the world-class, ancient crust-derived metal mineralization province (ε Nd (t) = -10 to -22) in South China. This suggests that rare metal mineral deposits are closely related to the evolved and reworked crust, no matter the age (young or ancient) of the crust.
In terms of magmatic-hydrothermal Pb-Zn-Ag ore deposits, their high spatial density in both the slight juvenile and slight ancient crustal provinces (Provinces III and IV, mainly ε Nd (t) = -3 to +3 with a peak at +1; Fig. 8) indicate that two factors, i.e. the ancient crust and multiple phases of reworking triggered by episodic enhancement of mantle activity, played a role in their formation. These reflect that many giant Mesozoic epithermal Pb-Zn-(Ag) deposits are distributed in the southern Great Xing'an Range of the eastern Altaids where more reworked crust occurs and some Late Paleozoic MVT-type Pb-Zn deposits are located on margins of cratons in the western Altaids. Previous studies have revealed that base metals (i.e. Pb, Zn and Ag) were readily exsolved during crystallization of the final phase of a composite granitic magma and the fluid transported metals to the distal parts of the ore-forming system (e.g. [99]). In such a condition, old crustal materials contribute metals to the granitic magmas. This is a prerequisite for regional Pb-Zn-(Ag) mineralization.
Several studies of both orogens and cratons also revealed that lithospheric architecture exerts crucial control on the formation of magmatichydrothermal ore systems [10][11][12]94,100,101]. Isotopic mapping reveals how the lithospheric architecture and crustal type (juvenile, ancient and reworked) control the type and distribution of ore deposits. Here, according to their deep material background or architecture, we propose that metallic ore mineralization or deposits can be grouped into at least three types: juvenile, mixed and ancient crustal architecture-related deposits, represented by the Li-Be, Ni-Ta, W-Sn and Pb-Zn-Ag, as well as (porphyry) Cu-Au deposits as three end members, respectively.
Orogens generally evolve from subduction/accretionary to collisional, and to intracratonic stages [66,87]. Recent studies revealed that collisional orogens can also produce worldclass mineralization belts in addition to subductional/accretionary orogens [97]; for example, in the Tethyan belt, remelting of sulfide-bearing, lower crustal cumulates of arc magmas associated with subduction-related porphyry Cu deposits produced giant collision-related porphyry Cu deposits [97]. The Altaids grew during long-term slab rollback in a retreating accretionary orogen, which formed giant extensional accretionary systems [25,26,30]. For example, the (south)westward rollback subduction/accretion in the Paleo-Asian Ocean formed the giant extensional accretionary systems (such as the Kazakhstan orocline) of the western Altaids, and eastward rollback subduction/accretion within the Mongol-Okhotsk Ocean formed the Tuva-Mongol accretionary systems (e.g. the Tuva-Mongol-Okhotsk orocline) in the eastern Altaids [27,43,61]. These extensional accretionary events produced a large-scale massive juvenile crust (or arc systems) and, significantly, this massive juvenile crust has been preserved through the development of oroclines [43,61]. Therefore, the Altaids can be viewed as the largest storage area and most typical 'fossils' of the juvenile crust in orogens worldwide. Our results are applicable to other types of orogens, particularly to the final continental collision and its control on mineralization.
Significantly, the preservation of large amounts of juvenile crust in accretionary systems may indicate that more giant ore deposits related to early subduction and accretion are present, such as in the Altaids.

CONCLUDING REMARKS
Isotopic mapping, based on 5507 whole-rock Nd and 39 514 (2443 samples) zircon Hf isotope data of felsic-intermediate-mafic igneous rocks as well as associated 1830 ore-deposit data for the Altaids has revealed the 3D lithospheric architecture characterized by the middle-lower crust and mantle. The juvenile crust (defined by ε Nd (t) > 0) comprises an area of ∼4 107 350 km 2 and a volume of ∼184 830 750 km 3 (assuming a crustal thickness of 40-50 km), accounting for ∼58% of the isotope-mapped area (∼7 010 375 km 2 ) of almost all the outcrops of the Altaids (∼8 745 000 km 2 ). The crustal growth rate is at least ∼0.22 km 3 per year. Compared with other global examples of Phanerozoic orogens, the Altaids hosts the largest volume, highest proportions and most rapidly produced juvenile crust, and it can be viewed as a 'fossiled' orogen with the largest preservation of juvenile crust in the world.
Isotopic mapping of the igneous rocks of 600-250 and 250-200 Ma revealed the 4D evolution of the crustal architecture. This indicates that the crustal architecture was mainly constructed during the syn-accretionary orogeny (600-250 Ma), which is indicative of a horizontal growth mechanism. Late Paleozoic-Mesozoic post-accretionary or intraplate igneous rocks (i.e. newly derived-mantle materials) record vertical crustal growth, which occurred in the eastern Altaids.
The crustal architecture of the Altaids reflects both the production and the preservation of massive juvenile crust, formed in the Paleo-Asian Ocean and the Mongol-Okhotsk Ocean tectonic domains. The juvenile crustal, slightly juvenile-reworked crustal and the slightly reworked crustal provinces controlled the Cu-Au, the Pb-Zn-Ag and the Li-Be, Nb-Ta, W-Sn ore deposits. A quantitative correlation between the isotopic provinces and ore-deposit types is proposed. According to the crustal architecture and background of deep compositions, we propose that the ore deposits can be grouped into three types: juvenile-crust-related, mixed-source-related and reworked-crust-related.